1. Field Of The Invention
This invention relates generally to fibrous web laminates suitable for use in articles such as disposable diapers, sanitary napkins, incontinence garments, and the like, and to a method and apparatus for making same. More specifically, the invention relates to a fibrous web laminate wherein a fibrous layer having a soft texture is laminated with a contiguous layer having a greater structural integrity such that the soft texture layer may be utilized as a skin-contacting surface and the contiguous layer thereto may provide mechanical strength and integrity to the laminate.
2. Description Of The Prior Art
U.S. Pat. No. 4,333,979 to M. A. Sciaraffa, et al. discloses a nonwoven web of thermoplastic fibers which is pattern bonded and further embossed to provide an increased effective thickness providing softness and bulk of the nonwoven material while retaining other desirable characteristics such as strength. The web is a spunbonded material composed of a closely-spaced point fused areas (constituting a spunbonded pattern) with the subsequently applied embossing pattern comprising much larger embossments. The resultant material is said to be highly effective as a liner for disposable products such as diapers, sanitary napkins and the like. The nonwoven web in this system is bonded by passage through a pattern nip formed by heated rolls, whereby individual compacted fused areas are formed occupying about 5 to 50% of the total web area with a density of about 50 to 3,200 fused areas per square inch. The further processing involves application of a gross embossing pattern imparting a substantially permanent deformation to the web in the form of a pattern of depressed areas. This gross pattern embossment is preferably obtained by passing the pattern-bonded web through a nip formed by a matched set of heated web embossing rolls. The gross pattern occupies an area of about 5 to 80% of the web surfaced with embossed pattern frequency in the range of from about 1 to 500 depressions per square inch. The disclosed webs have a basis weight in the range of from 0.4 ounces per square yard to 2.0 ounces per square yard, with web density being in the range of 0.08 to 0.20 gm/cc. The material of the nonwoven web includes meltspun fibers of thermoplastics such as polyolefins, polyethylene, polypropylene, polyesters, polyamides and composites thereof with cellulosic fibers. The patent describes the use of the disclosed nonwoven web as a topsheet of a diaper including a backsheet, an absorbent layer, and topsheet.
The teachings of the Sciaraffa patent relate to a doubly-embossed, single layer web. Because the web is a monolayer, the dual embossing steps will provide strengthening of the web structure, but such improvement in structural integrity is obtained at the expense of the softness and flexibility characteristics of the web stock from which the embossed product is made.
U.S. Pat. No. 4,374,888 to S. R. Bornslaeger discloses a nonwoven fabric laminate suitable for use in the manufacture of tents, outer garments, tarpaulins and the like, which comprises an outer spunbonded layer having ultraviolet radiation resistance imparted thereto, an intermediate microporous meltblown layer, preferably densified for resistance to liquid strike-through, and an inner spunbonded nonwoven layer treated for flame retardancy. The spunbonded layers preferably are formed with spotbonds, and have a basis weight of from about 0.5 to 5 ounces per square yard, with the intermediate meltblown layer having a basis weight of from about 0.5 to 2.0 ounces per square yard. Also disclosed is an embodiment wherein the spunbonded/meltblown/spunbonded laminate is pattern-bonded in a gross pattern occupying an area of 5 to 20% of the surface at a bond density of about 10 to 40 bonds per square inch. As shown in FIG. 4 of the patent, the laminate is spotbonded, and then pattern-bonded with a gross pattern of surface depressions being applied to both sides of the laminate; each layer of the laminate thus is correspondingly deformed by the gross pattern-bonding. The laminate is formed by lay-down of a spunbonded layer on a support belt, with the meltblown layer being formed directly on the spunbonded web, and a second spunbonded web then being applied to the meltblown layer to complete the composite, following which the entire composite is passed through a nip roll assembly for pattern-bonding. The laminate formed by the method of this patent suffers the same deficiency as the embossed web in the previously described Sciaraffa, et al. patent, in that the entire laminate is bonded, the spunbonded layers being dually bonded. Accordingly, the laminate by the inherent character of the pattern-bonding process has reduced flexibility and surface softness characteristics which, although not severely detrimental in the uses contemplated in the Bornslaeger patent, viz, in tents, outer garments, tarpaulins, and the like, render the laminate inadequate for the end-use application contemplated for the present invention.
U.S. Pat. No. 3,912,567 to R. J. Schwartz discloses a process for intermittent autogenous bonding of a continuous filament web. The web is passed directly through a nip formed by a smooth hard-surfaced roll and a roll containing raised points on its surface, both rolls being maintained at a temperature near the softening point of the filaments. This process is carried out such that the temperature of the web is not substantially increased before maximum pressure has been developed in the nip, but at maximum pressure is rapidly raised to effect surface fusion before a significant increase in filament crystallinity occurs. The purpose of the disclosed process is to provide two-sided surface abrasion resistance, with good physical strength properties, for high basis weight webs. The term "intermittent autogenous bonding" in this patent refers to bonding by application of heat to a substantially unbonded web at intermittent areas which define the upper and lower surfaces of intermittent regions of the web which are compressed under a pressure of at least about 2,000 psi. The process disclosed in this patent involves a two-sided monolayer web, and utilizes only one embossing step.
U.S. Pat. No. 4,069,078 to M. D. Marder, et al. discloses a finishing process for preparing nonwoven bonded sheets having high delamination strength and uniform appearance. The starting lightly consolidated sheet material is embossed by passage through a nip formed between two rolls, one of which has a multiplicity of bosses on substantially its entire surface, the bosses having a height of about 50-100% of the thickness of the sheet, with tips which have at least one dimension less than about 0.64 cm and the most prominent of which, in aggregate, form an area which is from 1-50% of the area of the surface of the roll. The resulting embossed sheet passes through a heating zone for fusion of the surface film-fibrils and then cools the sheet below its distortion temperature. Such heating/cooling steps being carried out for each of the two sides of the sheet to obtain a bonded sheet of suitable opacity. As in the previously described prior art, this patent discloses a process for a single nonwoven sheet of material, wherein a single embossing step is carried out.
U.S. Pat. No. 4,041,203 to R. J. Brock, et al. discloses a nonwoven material comprising an integrated mat of thermoplastic polymeric microfibers and a web of substantially continuous, randomly deposited, molecularly oriented filaments of the thermoplastic polymer. The microfiber mat and the continuous filament web are attached by autogenous bonding at intermittent discrete regions to utilize the continuous filament web as a load bearing constituent of the material which has desired strength characteristics and possesses a textile-like appearance, drape and hand. In manufacture, the continuous filament web is formed by laydown of spun filaments on a foraminous carrier belt and the integrated microfiber mat is brought into laminar contact with the continuous filament web to form the unbonded two-ply laminate. Subsequently, the bonding attachment between the mat and web is effected by passage of the composite laminate through a pressure nip formed between heated rolls, one of which contains a plurality of raised points on its surface. An intermittent bond pattern is preferably employed, so that the area of the web occupied by bonds after passage through the nip is about 5-50% of the surface area of the materials, the discrete bonds being present at a density of about 50-1000/in.sup.2. This patent discloses a multilayered web, but the layers are bonded by only a single thermal embossing step, so that it suffers the disadvantages referred to hereinabove, viz, loss of flexibility and soft surface texture.
U.S. Pat. No. 4,436,780 to H. W. Hotchkiss, et al. discloses a nonwoven wiper laminate including a relatively high basis weight intermediate layer of meltblown thermoplastic microfibers, e.g., of polypropylene, and outer lightweight layers of generally continuous filament thermoplastic fibers, e.g., spunbonded polypropylene, having a larger average diameter. In the manufacture of the disclosed laminate, the respective layers are superpositioned relative to one another and the tri-plied composite then is passed through the nip between a patterned roll and anvil roll to pattern bond same. Again, this patent discloses a multilayer composite wherein a single embossing step is utilized for the composite.
U.S. Pat. No. 3,949,130 to R. M. Sabee, et al. discloses a spunbonded web of continuous synthetic filaments having one side that is at least two times smoother than the opposite side, wherein the majority of filament cross-points within the web are fuse-bonded to one another during the spinning of the web. The laydown of the filaments on a collection surface results in flattening on the laydown side to produce a smooth surface, the other side of the web comprising filaments which are randomly entangled to form a rough surface. Such web is disclosed to be useful in disposable diapers or like articles in which the rough side of the web faces and serves to anchor an absorbent pad, preferably also acting as a moisture carrier for wicking moisture through the web and into the absorbent pad, and the smooth side of the web provides a surface for comfortable contact with the baby's skin.
As shown in FIG. 6 of this patent, there is a steep density gradient from the smooth side to the rough side of the disclosed web, the density for the smooth side being approximately 0.32 gm/cm.sup.3 and the density for the rough side being approximately 0.04 gm/cm.sup.3. Thus, the smooth side of the web is of higher density which increases the difficulty of liquid penetrating into the web, in contradistinction to the rough side which is of lower density and, as mentioned in the patent's Abstract, has utility for wicking moisture through the web and into the absorbent pad. The disclosed web has texture characteristics on the respective sides which are appropriate for the intended use, i.e., a smooth side against the baby's skin and a rough side which serves to prevent shifting or displacement of the absorbent pad disposed contiguous thereto, but such textural characteristics are at odds with the function of the web in providing fast and intensive wicking action for removal of liquid from contact with the baby's skin. Accordingly, it would be appropriate if the density characteristics of the respective smooth and rough sides were reversed relative to that shown in FIG. 6, with the smooth side adjacent the baby's skin having a lower density and the rough side having a higher density thereby enhancing the anchoring action of the rough side while providing a low density, high loft fluffy baby-side surface.
U.S. Pat. No. 4,377,615 to M. Suzuki, et al. discloses a nonwoven fabric comprising an upper layer having a substantially smooth surface and a lower layer having a density lower than that of the upper layer. The upper layer comprises hydrophobic fibers as a principal element, the denier of which is finer than the denier of the lower layer, and contains a larger amount of adhesive bonding materials than the lower layer. The lower layer comprises hydrophilic fibers and hydrophobic fibers, the denier of which is coarser than the denier of the upper layer, and contains a smaller amount of adhesive bonding materials than the upper layer.
The Suzuki, et al. patent states that the upper and lower layers do not indicate a state wherein the thickness of the nonwoven fabric is equally divided into two but rather a case wherein a state of a plurality of fibrous webs formed through mixing of different fibers are overlapped to constitute a nonwoven fabric. The nonwoven fabric in such case is divided into an upper layer having a relatively higher density and a lower layer having a relatively lower density, density referring to the amount of fibers and adhesive bonding materials in each of the upper and lower layers, being averaged. The patent discloses to use fibers of polyester, polypropylene, acrylic, rayon, acetate and the like for each of the respective layers. The adhesive bonding materials described in this patent include those comprising as a main component acrylic ester copolymers, consisting of monomers such as ethylacrylate, methylacrylate and/or butylacrylate, wherein ethylacrylate is a major component.
In the manufacture of the nonwoven fabric disclosed in the Suzuki, et al. patent, the fibers for the respective layers are prepared, formed into webs and piled up by a plurality of cards. The resulting web then is guided to a saturator, where the web is dipped in a low-solids binder emulsion. The amount of binder applied to the lower layer by the saturator is comparatively small with respect to the upper layer, which downstream of the dip zone is sprayed with a higher-solids binder emulsion, whereby the upper layer has a greater binder content than the lower layer. Subsequently, the web is passed through serial driers, and then guided into contact of its upper higher density layer with a smooth-surfaced cylinder, where the web is forcibly pressed against the cylinder's surface by a plurality of rolls, to cure the web and provide a substantially smooth surface on its upper surface.
In the specification of the Suzuki, et al. patent, at column 5, line 45 to column 6, line 21 thereof, the preparation of various sample webs according to the disclosed invention are described, wherein the respective layers are formed and "these webs are piled." There is no disclosure of any type of bonding of respective layers in the web to one another, contrariwise, the webs are merely piled relative to one another, so that there is only a mechanical entanglement of fibers therebetween at the interface of the two layers. Although a bonding medium subsequently is applied to the respective top and bottom surfaces of the composite web, it would be expected that consistent with the teachings of the patent, there is no flow-through or penetration from one layer to another, since same would destroy the density gradation which is stated to be an object of the fibrous web according to the patent, i.e., each of the respective layers having its own specific density as associated with the extent of the bonding medium applied thereto. Thus, the interface will be defined by a comparatively loose assemblage of fibers which have a low level of structural integrity relative to one another so that constituent layers of the web may shift relative to one another in use. Further, the fibrous web described by this patent has a significant deficiency in that a substantially smooth surface is provided on the outer surface of the higher-density, more extensively bonded layer. Accordingly, the smooth surface in operation will function to oppose wicking or penetration of liquid through the laminated web to the contiguously positioned absorbent pad (disposed against its smooth surface). In other words, while the fluffy back surface of the fibrous web of this patent is effective to sorb fluid from a baby's skin, there is presented to such sorbed fluid a transmission barrier in the form of the substantially smooth surface positioned between such fibrous web and the absorbent pad.